In the United States, large and persistent health disparities exist across the life course. Reducing these disparities is a top priority for policymakers and the public. Of particular importance, from a public health perspective, are disparities in chronic diseases. Collectively, chronic diseases-including cardiovascular disease and diabetes-represent the largest component of the total burden of disease and premature mortality in the United States. At the same time, chronic diseases are the major contributor to socioeconomic disparities in both the quantity and quality of life. Although chronic diseases are largely manifested during the prime adult ages and in old age, their precursors are apparent much earlier in the life course. In addition, chronic diseases in later life are related to health behaviors and outcomes at earlier ages. In this project, we will examine the emergence of chronic disease risk during the early adult years, focusing on disparities by socioeconomic status (SES). There are three specific aims. First, we will describe disparities in young adult biological indicators of chronic disease risk by childhood and current SES. By drawing on life course measures of educational attainment, income, occupational status, and job characteristics, this analysis will provide a more comprehensive description of SES disparities in chronic disease risk than previously available. Second, we will compare SES disparities in self-reported versus biological indicators of chronic disease risk. This aim will provide one of the first systematic assessments of the degree to which SES disparities in young adult health are underestimated due to reliance on self-reports. Third and finally, we will examine the impact of childhood SES and other early life socio-demographic factors-measured at multiple contextual levels and over time-on young adult disparities in chronic disease risk. We will use data from all four waves of the National Longitudinal Study of Adolescent Health (Add Health). The Add Health data are ideally suited for this study. Wave IV of Add Health will include multiple biological and behavioral health status measures from a diverse and nationally representative sample of 15,000+ young adults who have been followed since 1994-95. By integrating social, behavioral, and biological measures within a longitudinal design, these data will provide new opportunities to characterize the pathways leading to health disparities in early adulthood.